Mark Meynell thinks so, citing a piece by Abraham Piper which gives 6 reasons:
… to write
… to teach
… to recommend
… to interact
… to develop an eye for what is meaningful
… to be known
I particularly related to this bit from Piper:
Here is where a pastor has an outlet for whatever he didn’t get to say on Sunday. Your blog is where you can pass on that perfect analogy you only just thought of; that hilarious yet meaningful story you couldn’t connect to your text no matter how hard you tried; that last point you skipped over even though you needed it to complete your 8-point acrostic sermon that almost spelled HUMILITY.
I might add a 7th: creating a resource library, though it depends on why you're blogging. I use several blogs as online resource banks: for cartoons, for worship ideas, for news about the church, etc. One of the things I try to link to regularly is research and opinion surveys, as well as worship and mission resources, so that for myself (and hopefully for others) there is a one-stop site for the stuff which interests me, and perhaps others. Blogs which (unlike mine) stick to one subject, are great for this: if you want to mug up on emerging church, then Forgotten Ways and TallskinnyKiwi are great hubs for this. Not so much a library but all the signposts to places you want to go, together in one place.
On interacting, a blog means you get to interact with a much bigger 'parish', which I've found a good challenge. It makes me think a lot more about what I want to say, and has made me much more conscious of how minor some of our church debates are in the global context. It's for the church leader to decide how far that 'parish' goes - there are a billion debates on the web at any one time, and it's easy to divert yourself into these, instead of getting on with yet another sermon, doing that visit you've been putting off, or fixing your kids bike. Speaking of which.......